1. Field of the Invention
The present invention relates to a method for manufacturing a silicon-on-insulator (SOI) substrate having a so-called SOI structure in which a single crystal semiconductor layer is provided on an insulating surface, and a method for manufacturing a semiconductor device having the SOI structure.
2. Description of the Related Art
Integrated circuits have been developed, in which a semiconductor substrate called a silicon-on-insulator (hereinafter also referred to as “SOI”) having a thin single crystal semiconductor layer on an insulating surface is used instead of a silicon wafer manufactured in such a manner that an ingot of a single crystal semiconductor is thinly sliced. The integrated circuit using an SOI substrate has attracted attention as an integrated circuit which reduces parasitic capacitance between a drain of a transistor and the substrate and improves the performance of a semiconductor integrated circuit.
As a method for manufacturing SOI substrates, a hydrogen ion implantation separation method is known (e.g., see Patent Document 1). The hydrogen ion implantation separation method is a method in which hydrogen ions are implanted into a silicon wafer to form an embrittled region at a predetermined depth from a surface of the silicon wafer, and the silicon wafer is separated at the embrittled region, whereby a thin silicon layer is bonded to another silicon wafer. In addition to the heat treatment for separation of a silicon layer, it is necessary to perform heat treatment in an oxidizing atmosphere to form an oxide film over the silicon layer, remove the oxide film, and perform heat treatment at 1000° C. to 1300° C. to increase bonding strength.
On the other hand, a semiconductor device in which an insulating substrate made of high heat resistance glass or the like is provided with a silicon layer is disclosed (e.g., see Patent Document 2). In this semiconductor device, an entire surface of crystallized glass whose strain point is greater than or equal to 750° C. is protected by an insulating silicon film, and a silicon layer obtained by a hydrogen ion implantation separation method is bonded to the insulating silicon film.
On the surface of the silicon layer obtained by a hydrogen ion implantation separation method, there exists defects due to an ion implantation step or the like for forming an embrittled region. Therefore, a technique of removing the defects by vapor-phase etching is disclosed (see Patent Document 3).